The objectives of this study are to examine the effect of certain beta-adrenergic anti-labor drugs on uterine and umbilical blood flows, maternal and fetal heart rates, arterial pressures, arterial blood gases and plasma glucose concentrations, and to evaluate the effect of these agents on maintenance or restoration of fetal well-being. Pregnant Dorset sheep are operated between 125-145 days gestation (term is 145 days). Electromagnetic flow probes and catheters are placed on/in pertinent maternal and fetal vessels and a chronic preparation is obtained. After a minimum of 96 hours to allow for recovery and reestablishment of maternal and fetal homeostasis, the test drug (ritodrine HCl, salbutamol, or fenoterol (Th1165a) is infused into a peripheral maternal vein. It is administered at a constant dose for 6 hours. Physiologic measurements are then obtained utilizing the surgically placed flow probes and catheters. BIBLIOGRAPHIC REFERENCES: Ehrenkranz, R.A., Hamilton, L.A., Brennan, S.C., Oakes, G.K., Walker, A.M. and Chez, R.A.: Effects of Salbutamol and Isoxsuprine on Uterine and Umbilical Blood Flow in Pregnant Sheep. Amer. J. Obstet. Gynec. 1977 (In Press). Brennan, S.C., McLaughlin, M.K., Hamilton, L.A. and Chez, R.A.: Effects of Prolonged Infusions of Beta-Adrenergic Agonists on Uterine and Umbilical Blood Flow in Pregnant Sheep. Amer. J. Obstet. Gynec. 1977 (In Press).